1. Field of the Invention
This invention relates to a process for the preparation of phenyldichlorophosphine. More particularly, this invention relates to a process for the vapor phase preparation of phenyldichlorophosphine at temperatures from about 100.degree. C. to about 145.degree. C. in the presence of a catalyst consisting essentially of aluminum metal and an activating amount of aluminum chloride.
Phenyldichlorophosphine is a very useful intermediate compound in organic synthesis. It may be used to prepare various phosphorus-containing insecticides and to prepare the corresponding phosphonous acid, C.sub.6 H.sub.6 P(OH).sub.2. Extensive quantities of phenyldichlorophosphine are used each year for these purposes.
2. Description of the Prior Art
Various processes for the preparation of aryldihalophosphines are known in the art. The preparation of aryldichlorophosphine, inter alia, is described in U.S. Pat. No. 3,954,859. In this process, an aromatic hydrocarbon selected from benzene, toluene, and xylene is reacted with phosphorus trichloride in the presence of a crystalline aluminosilicate zeolite in the hydrogen form catalyst at a temperature from 147.degree. to 475.degree. C. In this reaction, benzene and phosphorus trichloride yield phenyldichlorophosphine.
In U.S. Pat. No. 3,864,394 is described a process wherein phenyldichlorophosphine (phenylphosphonous dichloride) is prepared by reacting chlorobenzene, phosphorus trichloride, and elemental phosphorus in an autoclave at a temperature from about 275.degree. C. to about 400.degree. C. for a period of time from about 0.25 hour to about 30 hours.
U.S. Pat. No. 3,210,418 discloses the preparation of phenyldichlorophosphine by reacting benzene with phosphorus trichloride at a temperature of 725.degree. C. in the presence of a homogeneous gaseous catalyst, for example, molecular oxygen, halogens, or nitrogen oxides, which function as a free radical promoter.
In U.S. Pat. No. 3,057,917 is described a process for preparing, inter alia, arylhalophosphines which comprises reacting an aryl halide, in the vapor phase, with red phosphorus in the presence or absence of a metal catalyst selected from the group consisting of copper, nickel, silver, tin, antimony, and alloys of copper with at least one other metal of the group of metals. The aryldihalophosphine reportedly is the predominant species.
U.S. Pat. No. 3,029,282 describes a process for the preparation of phenyldichlorophosphine wherein benzene and phosphorus trichloride are reacted at temperatures of at least 350.degree. C. in the presence of chlorobenzene. The presence of chlorobenzene reportedly increases the reaction rate, decreases decomposition products, and improves the quality of the phenyldichlorophosphine.
In Japanese Pat. No. Sho 44[1969]-3354 a process for the preparation of phenyldichlorophosphine is described wherein benzene and phosphorus trichloride are reacted at a temperature of 550.degree. C. to 850.degree. C. in the presence of carbon tetrachloride.
Finally, in an article in Organic Syntheses, Coll. Vol. 4, 784-785 (1963), there is disclosed a process for the preparation of phenyldichlorophosphine which comprises reacting in the liquid phase a homogeneous solution of benzene, phosphorus trichloride, and aluminum chloride at reflux temperatures, and treating the resulting hot reaction mixture with phosphorus oxychloride.
Although these prior art processes generally provide the desired product, they nevertheless are limited in their application. Principal among these limitations, are the drastic and severe reaction conditions which must be employed which leads to the substantial production of decomposition products. The discovery of the relatively low temperature, vapor phase process of the present invention is therefore believed to be a decided advance in the state of the art.